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Water Treatment Plant Operator Test Questions > Lime Softening > Flashcards

Lime Softening Flashcards

1
Q

⭐ The capacity to neutralize acids is called

A

Alkalinity

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2
Q

⭐ The amount of acid that is added to water ( liquid) to lower the pH to 4.5 determines what parameter?

A

Alkalinity

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3
Q

Water with a hardness of more than a 100 mg/L is called?

A

Hard water

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4
Q

⭐ Total hardness is the sum of what salts?

A

Calcium and magnesium

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5
Q

Calcium and magnesium are defined as what type of hardness?

A

Carbonate hardness

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6
Q

Carbonate hardness is called

A

Temporary hardness because it is easy to remove

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7
Q

⭐ if the total hardness of the water is less than the alkalinity, what kind of hardness is present in the water?

A

Carbonated hardness

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8
Q

⭐ The total hardness is greater than the alkalinity. Subtracting. The alkalinity from the harness gives you what type of hardness?

A

Non-carbonate hardness

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9
Q

⭐ non-carbonate hardness is called

A

Permanent hardness because it is difficult to remove

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10
Q

⭐ The alkalinity in question 8 is equal to what type of hardness

A

Carbonate hardness

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11
Q

Total hardness is the sum of what two types of hardness

A

Carbonate and non-carbonate hardness or temporary and permanent hardness or calcium and magnesium

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12
Q

⭐ a pure substance composed of two or more elements whose composition is constant is called?

A

A compound

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13
Q

CaO is the shorthand symbol for what substance?

A

Lime or quick lime?

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14
Q
A

Slaked lime or hydrated lime

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15
Q

⭐ what is the first reaction that takes place when you add slake lime to raw water?

A

Carbon dioxide (CO2) is removed

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16
Q

⭐ what is a byproduct of slake lime?

A

Heat

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17
Q

⭐ what is the simplest test to determine if water is hard?

A

Soap

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18
Q

Why do we soften water?

A

Hard water causes scaling and boiler and chiller problems. Hard water also causes taste and odor problems and also stains laundry

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19
Q

⭐ what is added to lime softening to remove non-carbonated hardness

A

Soda ash

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20
Q

⭐ what is methyl orange alkalinity?

A

Total alkalinity

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21
Q

⭐ what happens when lime is added to water

A

Lime raises the pH and alkalinity

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22
Q

⭐ when lime raises the water pH to 10, what reaction takes place?

A

Soluble calcium forms insoluble precipitates

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23
Q

⭐ what is the SMCL for pH?

A

6.5- 8.5

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24
Q

⭐ what method is used to lower the pH?

A

Recarbonation or split treatment

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25
Q

⭐ water treatment plants have to add excess lime to remove magnesium hardness. What treatment method is used to lower the cost by reducing the amount of lime added to remove magnesium?

A

Split treatment

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26
Q

⭐ why must we lower the pH of the water after lime has formed hardness precipitates?

A

To reduce the scaling tendencies of water or to precipitates hardness

27
Q

⭐ how is pin floc removed during water treatment?

A

Recarbonation or filtration?

28
Q

⭐ when you use 0.02 N sulfuric acid to titrate a water sample to a pH of 8.3, what parameter is being measured?

A

P alkalinity ( phenolphthalein alkalinity)

29
Q

⭐ when you use 0.02N sulfuric acid to titrate a water sample to a ph of 4.5, what parameter is being measured?

A

Total alkalinity or methyl orange alkalinity

30
Q

What does NPDES mean?

A

National pollutant discharge elimitation system

31
Q

⭐ what causes carbonate hardness?

A

Alkalinity

32
Q

⭐. What causes non-carbonate hardness?

A

Sulfates

33
Q

⭐. What is the SMCL for sulfates?

A

250 mg/L

34
Q

⭐. Why are water treatment plant operators concerned with sulfates?

A

They have a laxative effect and they cause scaling

35
Q

⭐. Below a water pH of 8.3, what type of alkalinity is absent?

A

P alkalinity (phenolphthalein alkalinity)

36
Q

What is a common problem found in home water heaters that use a lime softened water?

A

Scaling of the water heaters heating element because calcium carbonate is not stable in hot water

37
Q

⭐. What are some advantages of line softening?

A

Corrosion control, iron amnesium removal, disinfection due to high pH, taste and odor reduction, removal of radioactivity

38
Q

⭐ All the water treatment plants must use what book to determine the method of analysis for any parameter the WTP is required to analyze for?

A

Standard methods for examination of water and wastewater

39
Q

⭐ what test is used to measure the intensity of the basic or acidic condition of water?

A

pH

40
Q

⭐. What test is used to measure the hydrogen ion activity in a liquid?

A

pH

41
Q

⭐. What is the numerical range of pH?

A

0 to 14

42
Q

⭐ the logarithm (base 10) of the reciprocal of the hydrogen ion activity is called ?

A

pH

43
Q

⭐. When alum is added to the water, what happens to the pH?

A

pH goes down

44
Q

⭐. When the amount of alum is decreased during treatment, what adjustment is usually made to the Lime dosage

A

Lime dosage is also decreased

45
Q

⭐ when the amount of alum is increased during treatment, what adjustment is usually made to the lime dosage?

A

Lime dosage is also increased

46
Q

⭐ below a pH of 8.3 what is the only alkalinity usually present in the water?

A

Bicarbonate alkalinity

47
Q

⭐. What is the formula for hydroxide alkalinity (OH)?

A

2P-T

48
Q

If the PA is 84 and the TA ( total alkalinity is 160) , what is the OH?

A

8 (2x84(PA)- 160( TA)=8

49
Q

Adding the bicarbonate, carbonate, and hydroxide alkalinity gives you what result?

A

Total alkalinity

50
Q

⭐Below a pH of 4.5, what is usually present in the water?

A

Carbon dioxide CO2 and no Alkalinity

51
Q

⭐. When lime is added to water, bicarbonate alkalinity is converted to?

A

Carbonate alkalinity which allows the calcium precipitate as calcium carbonate

52
Q

⭐. When excess lime is added to water, PA is converted to?

A

OH! ( Hydroxide) which allows magnesium to precipitate

53
Q

⭐. Lime softening alone can reduce water hardness to what level?

A

30 to 40 mg per liter

54
Q

⭐. During reCarbonation what is added to water to lower the pH and alkalinity?

A

Carbon dioxide CO2

55
Q

⭐. Carbon dioxide (CO2) is added where during the recarbonation process

A

Before filtration

56
Q

⭐. In split treatment, how much raw water is bypassed?

A

20%

57
Q

⭐. What happens to the pH when sodium aluminate is used as a coagulant?

A

pH goes up

58
Q

⭐. If sodium aluminate is substituted for alum, what will happen to the lime dosage?

A

Lime dosage will be decreased

59
Q

⭐ what is used to reduce the pH and alkalinity in treatment water?

A

Carbon dioxide CO2

60
Q

What two chemicals should not be added to the same conveyor belt?

A

Lime and aluminum. They are explosive when combined

61
Q

What is a disadvantage of recirculating dewatered sludge supernatant?

A

Magnesium content of water increase

62
Q

⭐. Where is lime Sludge disposed of?

A

Sanitary landfills

63
Q

⭐. Large amounts of what chemical in lime sludge makes it difficult to dewater?

A

Magnesium ( less than two to one ratio of Ca to Mg is difficult to dewater)

Water Treatment Plant Operator Test Questions (16 decks)

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